This invention relates to the equipment for supplying separate slurries of fibrous stock to the separate chambers of a multi-ply fibrous web former such as disclosed in U.S. Pat. Nos. 3,598,696, 3,839,143 and 3,923,593, all of which are assigned to the assignee of this application. Such formers pertain to the substantially simultaneous formation of a multi-ply fibrous product, such as paper board, on a paper making machine.
Historically, multi-ply paper board has been manufactured on cylinder-type machines wherein each layer is applied sequentially to a previously formed web layer to build the composite board up to the required thickness. Each cylinder vat is provided with its own pump to form a new layer on the oncoming web.
In order to produce paper board faster, formers such as disclosed in the aforementioned patents have been conceived and each of the chambers to make the separate layer of the product has been supplied with separate stock supply equipment, including separate white water silos, fan pumps and related piping.
Such fan pumps are commonly used in the manufacture of single ply paper to supply the headbox, or "former", as high pressure hydraulic headboxes are sometimes called, with a water-fiber slurry composed of about 0.5 percent fibers. Thus, to manufacture a paper web at speeds up to 5,000 fpm, or greater, a fan pump having a large capacity and which consumes large amounts of power is required.
However, simultaneously pumping the stock slurry for each ply of a multi-ply web with a separate fan pump greatly increases the operating expenses and initial capital requirements. Often, in a three layer composite web, the inner layer may comprise a relatively cheap, low strength, high bulk material containing recycled fibers, ash and coating residue while the outer layers are comprised of high strength, virgin fibers. Thus, heretofore, it was considered necessary to supply separate equipment, including motors, fan pumps and white water silos, for each of the various plies produced in a multi-ply former.